diff --git a/src/clayterm.c b/src/clayterm.c
index 8b8ae69..b52c8f2 100644
--- a/src/clayterm.c
+++ b/src/clayterm.c
@@ -75,6 +75,11 @@ struct Clayterm {
    * re-init, so the values survive resize updates. */
   uint32_t colors; /* max_colors evidence; §7.1 baseline is 256 */
   int truecolor;   /* positive truecolor evidence */
+  /* Terminal-default colors for compositing destinations (renderer-spec
+   * §7.9), resolved by the host: reported theme > createTerm
+   * defaultTheme > black background / white foreground. 24-bit RGB. */
+  uint32_t default_bg;
+  uint32_t default_fg;
   /* Emission tier, resolved once per reduce. last_tier detects tier
    * changes, which force a complete redraw (color-encoding-spec CI-5). */
   int tier;
@@ -857,12 +862,16 @@ int error_message_ptr(struct Clayterm *ct, int index) {
 }
 
 /* Push host-held color capability evidence into the instance
- * (color-encoding-spec §4.2). Called once after init and after update()
- * folds capability events that change either value; re-pushed by the
- * host after any re-init so the values survive resize updates. */
-void set_capabilities(struct Clayterm *ct, uint32_t colors, int truecolor) {
+ * (color-encoding-spec §4.2; renderer-spec §7.9 defaults). Called once
+ * after init and after update() folds capability events that change any
+ * value; re-pushed by the host after any re-init so the values survive
+ * resize updates. */
+void set_capabilities(struct Clayterm *ct, uint32_t colors, int truecolor,
+                      uint32_t default_bg, uint32_t default_fg) {
   ct->colors = colors;
   ct->truecolor = truecolor ? 1 : 0;
+  ct->default_bg = default_bg & 0x00FFFFFF;
+  ct->default_fg = default_fg & 0x00FFFFFF;
 }
 
 struct Clayterm *init(void *mem, int w, int h) {
@@ -890,7 +899,9 @@ struct Clayterm *init(void *mem, int w, int h) {
       .lastbg = 0xffffffff,
       .lastx = -1,
       .lasty = -1,
-      .colors = 256, /* §7.1 baseline until the host pushes evidence */
+      .colors = 256,          /* §7.1 baseline until the host pushes evidence */
+      .default_bg = 0x000000, /* §7.9 fallback: black background */
+      .default_fg = 0xffffff, /* §7.9 fallback: white foreground */
       .last_tier = -1,
   };
 
diff --git a/src/clayterm.h b/src/clayterm.h
index 531356f..4f1ad5f 100644
--- a/src/clayterm.h
+++ b/src/clayterm.h
@@ -12,7 +12,8 @@ struct Clayterm;
 /* WASM exports */
 int clayterm_size(int w, int h);
 struct Clayterm *init(void *mem, int w, int h);
-void set_capabilities(struct Clayterm *ct, uint32_t colors, int truecolor);
+void set_capabilities(struct Clayterm *ct, uint32_t colors, int truecolor,
+                      uint32_t default_bg, uint32_t default_fg);
 void reduce(struct Clayterm *ct, uint32_t *buf, int len, int mode, int row,
             float deltaTime);
 char *output(struct Clayterm *ct);
diff --git a/term-native.ts b/term-native.ts
index f4e7b7f..db44015 100644
--- a/term-native.ts
+++ b/term-native.ts
@@ -26,10 +26,14 @@ const CLAY_DEFAULT_MAX_ELEMENT_COUNT = 8192;
 const MAX_FIXED_ELEMENT_WIRE_BYTES = 116;
 
 /** Color capability evidence the renderer consumes for emission
- * (color-encoding-spec §4.2). */
+ * (color-encoding-spec §4.2). The default colors are the §7.9 chain's
+ * resolution (reported theme > defaultTheme > black/white), packed as
+ * 24-bit RGB. */
 export interface ColorCaps {
   colors: number;
   trueColor: boolean;
+  defaultBg: number;
+  defaultFg: number;
 }
 
 export interface Native {
@@ -46,11 +50,16 @@ export interface Native {
   update(w: number, h: number): void;
   /**
    * Push color capability evidence into the renderer. Called by the
-   * host after update() folds capability events that change either
-   * value (color-encoding-spec §4.2); re-pushed internally after any
-   * re-init so the values survive resize updates.
+   * host after update() folds capability events that change any value
+   * (color-encoding-spec §4.2); re-pushed internally after any re-init
+   * so the values survive resize updates.
    */
-  setCapabilities(colors: number, trueColor: boolean): void;
+  setCapabilities(
+    colors: number,
+    trueColor: boolean,
+    defaultBg: number,
+    defaultFg: number,
+  ): void;
   reduce(
     ct: number,
     buf: number,
@@ -119,7 +128,13 @@ export async function createTermNative(
     ): void;
     output(ct: number): number;
     length(ct: number): number;
-    set_capabilities(ct: number, colors: number, truecolor: number): void;
+    set_capabilities(
+      ct: number,
+      colors: number,
+      truecolor: number,
+      default_bg: number,
+      default_fg: number,
+    ): void;
     Clay_SetPointerState(vec: number, down: number): void;
     pointer_over_count(): number;
     pointer_over_id_string_length(index: number): number;
@@ -151,6 +166,8 @@ export async function createTermNative(
       statePtr,
       currentCaps.colors,
       currentCaps.trueColor ? 1 : 0,
+      currentCaps.defaultBg,
+      currentCaps.defaultFg,
     );
   }
 
@@ -187,8 +204,13 @@ export async function createTermNative(
     update(uw: number, uh: number): void {
       layout(uw, uh);
     },
-    setCapabilities(colors: number, trueColor: boolean): void {
-      currentCaps = { colors, trueColor };
+    setCapabilities(
+      colors: number,
+      trueColor: boolean,
+      defaultBg: number,
+      defaultFg: number,
+    ): void {
+      currentCaps = { colors, trueColor, defaultBg, defaultFg };
       pushCaps();
     },
     reduce: ct.reduce,
diff --git a/term.ts b/term.ts
index 8d71a77..c14d179 100644
--- a/term.ts
+++ b/term.ts
@@ -14,6 +14,17 @@ export interface TermOptions {
    * baseline.
    */
   terminfo?: TerminalInfo;
+  /**
+   * Fallback terminal default colors for compositing destinations
+   * (renderer-spec §7.9). Used when the terminal has not reported its
+   * own theme; does not change term.capabilities.theme, which holds
+   * only reported colors. Defaults to a black background and a white
+   * foreground.
+   */
+  defaultTheme?: {
+    foreground?: Rgb;
+    background?: Rgb;
+  };
 }
 
 /**
@@ -94,6 +105,23 @@ function runtimeFromStatic(caps: Capabilities): RuntimeCapabilities {
   });
 }
 
+/** Resolve the §7.9 terminal-default chain: reported theme >
+ * defaultTheme > a black background and a white foreground. Packed as
+ * 24-bit RGB for the renderer. */
+function defaultColors(
+  fallback: TermOptions["defaultTheme"],
+  reported: { theme: RuntimeCapabilities["theme"] } | undefined,
+): { defaultBg: number; defaultFg: number } {
+  let bg = reported?.theme.background ?? fallback?.background ??
+    { r: 0, g: 0, b: 0 };
+  let fg = reported?.theme.foreground ?? fallback?.foreground ??
+    { r: 255, g: 255, b: 255 };
+  return {
+    defaultBg: (bg.r & 0xff) << 16 | (bg.g & 0xff) << 8 | (bg.b & 0xff),
+    defaultFg: (fg.r & 0xff) << 16 | (fg.g & 0xff) << 8 | (fg.b & 0xff),
+  };
+}
+
 export interface RenderOptions {
   mode?: "line";
   row?: number;
@@ -162,7 +190,7 @@ export interface Term {
 }
 
 export async function createTerm(options: TermOptions): Promise<Term> {
-  let { width, height, terminfo } = options;
+  let { width, height, terminfo, defaultTheme } = options;
 
   let seed = terminfo?.capabilities ?? {
     colors: 256,
@@ -177,6 +205,7 @@ export async function createTerm(options: TermOptions): Promise<Term> {
   let native = await createTermNative(width, height, {
     colors: seed.colors,
     trueColor: seed.trueColor,
+    ...defaultColors(defaultTheme, undefined),
   });
   let { memory } = native;
 
@@ -310,15 +339,24 @@ export async function createTerm(options: TermOptions): Promise<Term> {
         }
 
         currentCaps = next;
-        // Folded evidence changed the renderer's color capabilities:
-        // push it so the next render resolves the new tier
-        // (color-encoding-spec §4.2). The tier change itself forces a
-        // complete redraw on the next transaction (§6.4).
+        // Folded evidence changed the renderer's color capabilities or
+        // theme: push it so the next render resolves the tier and the
+        // compositing defaults (color-encoding-spec §4.2; renderer-spec
+        // §7.9 theme changes). The update transaction itself emits no
+        // bytes; the next transaction picks the change up.
+        let colors = defaultColors(defaultTheme, next);
         if (
           next.colors !== native.caps.colors ||
-          next.trueColor !== native.caps.trueColor
+          next.trueColor !== native.caps.trueColor ||
+          colors.defaultBg !== native.caps.defaultBg ||
+          colors.defaultFg !== native.caps.defaultFg
         ) {
-          native.setCapabilities(next.colors, next.trueColor);
+          native.setCapabilities(
+            next.colors,
+            next.trueColor,
+            colors.defaultBg,
+            colors.defaultFg,
+          );
         }
         if (bytes.length) out.push(bytes);
       }
diff --git a/test/width.test.ts b/test/width.test.ts
index 267ca64..9478d50 100644
--- a/test/width.test.ts
+++ b/test/width.test.ts
@@ -60,6 +60,8 @@ describe("width", () => {
     let native = await createTermNative(10, 3, {
       colors: 256,
       trueColor: false,
+      defaultBg: 0x000000, // §7.9 fallback: black background
+      defaultFg: 0xffffff, // §7.9 fallback: white foreground
     });
 
     // TextEncoder never produces surrogate bytes, so pack a placeholder